1. Field of the Invention
The invention relates to a method for determining the viscosity of a medium with a Coriolis mass flowmeter, wherein the Coriolis mass flowmeter has at least two measuring tubes that medium can flow through and a measuring device, wherein the measuring device has at least two actuator assemblies, wherein a measuring tube plane is defined by the measuring tube central axis and wherein the actuator assemblies are arranged on both sides of the measuring tube plane and outside of the measuring tube plane.
2. Description of Related Art
Coriolis mass flowmeters are known in a plurality of designs in the prior art. Differences include, on the one hand, for example, the number of measuring tubes of an instrument, and on the other hand, whether the measuring tubes are bent or straight. In order to measure the mass flow, the measuring tubes are excited to oscillation; wherein the input and output ends of the measuring tube oscillate in phase to one another without flow. With flow, inertial force from Coriolis acceleration causes a phase shift within the oscillation of the measuring tubes, which is detected by sensor assemblies and can be evaluated as a measuring signal for the mass flow.
Furthermore, Coriolis mass flowmeters are known from the prior art, for example, from U.S. Pat. No. 6,006,609, having just a single measuring tube, wherein the measuring tube can be used, on the one hand, for detecting mass flow in that oscillation is shifted perpendicular to its axial length, the tube also oscillates here in an oscillation plane—for measuring mass flow. On the other hand, the measuring tube can be shifted into torsional oscillation, wherein information about the viscosity of the medium flowing through the measuring tube can be drawn by evaluating this torsional oscillation. The measured physical correlations needed for this have been known for a long time and are not a central object of consideration. At any rate, torsional oscillation causes shear forces acting in the circumferential direction to be created through the measuring tube walls, through which oscillation energy of the torsional oscillation is detracted and dissipated in the medium. In order to sustain the torsional oscillation of the measuring tube, it is necessary that additional excitation energy is supplied to the measuring tube. The viscosity of the medium can be determined from the value of the additionally supplied excitation energy for sustaining the torsional oscillation by means of the measuring sensor.
The Coriolis mass flowmeters known from the prior art and suitable for measuring the viscosity of a medium, however, have one disadvantage, that elaborate measuring devices are required for detecting the torsional oscillation as, for example, in U.S. Pat. No. 6,006,609.